1. Field of the Invention
This invention relates generally to internal combustion engines and accessories therefor and, more specifically, to a Calibration Method for Air Intake Tracts for Internal Combustion Engines.
2. Description of Related Art
For the sake of this discussion, the phrase “intake system” is being used to describe the ducting and accessories that feed air to an internal combustion engine prior to the throttlebody, including the large duct, filter, and any other parts thereof. FIG. 1 is a schematic diagram of an internal combustion engine's intake tract. The mass airflow sensor 26 and emissions/central computer 28 are depicted here for reference, but will be described more fully in connection with FIG. 2 and beyond.
The original equipment manufacturer (OEM) intake system 14 on a typical production vehicle consists of an air inlet 23 leading to a resonator 16, a substantial amount of plastic duct work 18, a large metal or plastic air filter canister 20, a paper air filter element 22, and a rubber accordion hose 24 between the filter canister and the throttlebody. Usually, the intake system 14 will pick up air from behind the vehicle's fender or bumper, from the leading end of the plastic duct work and resonator. This design is the most favorable for OEM systems because the air taken in by the intake system is cooler than if the air was being taken from inside the engine compartment. Cooler air allows the engine to make more power than hot air. In cases where the intake system takes air from inside the engine compartment, lower-power performance from the engine should be expected.
Even if the OEM intake system is taking its air from outside the engine compartment, there still are performance-sapping design aspects to virtually all OEM intake system designs. First, the resonator 16 and the plastic duct work 18 tend to be very restrictive to air flow. These pieces are designed to reduce intake sound (i.e. engine sound), and therefore performance is not the priority. Performance can be improved by eliminating the resonator 18, reducing the ductwork length and increasing the ductwork diameter.
Second, the OEM paper filter element 22 is usually a very low-cost, disposable unit. Paper elements typically restrict flow more than cotton gauze or cloth. “Aftermarket” cotton gauze or cloth filters provide a great deal more air flow with the added advantage that they are reusable and can be washed, re-oiled, and reinstalled in the intake tract for ten years of use, or more.
Third, the accordion hose 24 between the filter canister 20 and the throttlebody 25 does not encourage very good air flow. The ribs of the hose 24 extend into the air flow channel and cause turbulence, thereby reducing and/or corrupting the airflow in this section of the intake tract 14.
One of the most popular horsepower-improving aftermarket products for vehicles is the “cold air intake” system. As the name suggests, one thing that these systems do is to locate (or relocate) the front end of the air intake tract to a location that is outside of the engine compartment (many times behind the vehicle's bumper).
The most common and most effective cold air intake 30 design is depicted in FIG. 2. These systems use sections of mandrel bent pipe 32, connected with turbo hose connectors 34, leading from the throttlebody 25 and out of the engine compartment to the area behind the bumper or behind the fender, where a cone filter 36 is fitted to the pipe 32 to draw in cool air from outside the engine compartment. The combination of the cooler intake air and the reduction in flow resistance results in significant power increase. In addition, the modified intake tract 30 will typically be three or more feet in length, causing it to effectively act as an extension of the intake manifold of the engine, almost as if it were a header for the intake side of the engine, improving low and mid range torque.
Furthermore, the added length of the pipe work also encourages something called “laminar air flow effect” whereby the air passing through the pipe is unobstructed and begins to act somewhat more like a liquid than a gas, gaining momentum as it passes down the pipe and resisting anything that would stop its flow. This is known as an air ramming effect.
While the power improvements made available by cold air intake systems 30 are well-known, so are the problems associated with them. First, the OEM intake tract 14 has a “Mass Airflow Sensor” (MAFS) 26 attached to it. The MAFS 26 is a very important sensor that detects the airflow in the intake tract and reports this information to the engine's central computer 28. The central computer 28 uses this information to adjust the combustion performance factors of the engine so that the engine runs cleanly (low emissions) and smoothly.
It has been common to receive “check engine” lights when installing aftermarket cold air intake systems in vehicles because the flowrate of the incoming air has increased so much (because the theory has always been “more is better”) that the values are outside those expected by the central computer 28. In fact, some vehicle models and/or intake systems suspected to actually cause damage to the engine.
One solution for the check engine light problem has been to replace the MAFS 26 with a non-OEM unit that will scale down input to the central computer 28 so that it will be within the expected range. This is dangerous and further may actually void the manufacturer's warranty on the engine. The only other solution has been to reprogram (or “tune”) the central computer 28 so that the MAFS 26 input is within the newly-programmed computer's range. This approach, while effective, only serves to add cost and uncertainty to the intake system “upgrade.”
What is really needed is an aftermarket intake system and method for custom-designing such system so that the OEM MAFS and central computer system can be retained after the installation of the high-performance cold air intake system.